The invention is directed to an apparatus for fastening electrical parts, especially measurement converters, into the connecting heads of electrical thermometers by means of fasteners consisting of screws, a casing and a helical spring.
With electrical thermometers, such as resistance thermometers or thermocouples, the connecting elements for the connecting of the thermoprobe with the recording instrument for the most part are mostly placed in a special housing, the connection head. This connection head consists of a base body and a cover which is connected with the base body by means of a flap hinge or screws.
The base body of the connecting head is normally firmly joined with the protective tube of the electrical thermometer via a screw coupling. The actual measuring probe of the thermometer is located inside the protective tube either fixedly joined with this or loosely inserted as a measuring insert. The free ends of the measuring probe are located in the connecting head and are frequently constructed as screw connections, which are mounted on a carrier body, for example made of porcelain. The base body also carries a cable screw connection through which the connecting cable extends.
The inner space of the connecting head is customarily only insignificantly larger than is needed by the space requirement of the connecting elements of the measuring probe. Therefore it is not normally possible to accommodate additional structural elements as, for example, measuring converters in standard connecting heads without changes in construction.
The temperature probes customarily are connected by screws with the base body of the connecting head. Thereby it is advantageous to use fasteners consisting of screws, a casing and helical spring in order that there can be obtained a closed form and good heat conducting contact between probe and protecting tube at the bottom of the protecting tube.
It is known to include an additional electrical device, as, for example, a measuring converter, in the connection head by eliminating mounting on the carrier and mounting the part directly on the bottom plate of the temperature probe which is located within the connecting head. The mounting is carried out normally with screws from the underside of the bottom plate. However, this has the disadvantage that the part can only be removed with difficulty if the bottom plate, e.g., through corrosion, is jammed tight in the connecting head and there is no possibility of getting near to the fastening screws on the underside of the bottom plate.
Therefore it is an object of the present invention to provide an apparatus for fastening an electrical device, especially of measuring converters, into the connecting head of an electrical thermometer by means of fasteners consisting of screws, a casing and helical spring with which the part can be accommodated in easily changeable manner in the spatially limited inner space of the connection head.
SUMMARY OF THE INVENTION
This object is attained according to the invention by providing the fastener fitted electrical device disposed within the apparatus with bores having one or more pins on the interior thereof and a casing in which the helical spring is located and having in the upper area a J-shaped notch or channel engageable with the pin and at the lower edge is provided with a flange.
Advantageously the disposition of this casing is arranged so that the flange of the casing is located under the end winding of the helical spring so that the casing end is pressed on the bottom plate of the temperature probe. It is also advantageous if the casing is open on one side in the lower area so that it can be subsequently slid over the helical spring and also can be removed in the same way.
The electrical device is provided with one or more bores passing through it, which bores have a diameter and arrangement to receive the fasteners of the bottom plate which are fitted on the base body of the connection head. The fasteners in this case may comprise screws, the casing and the helical spring or springs which is arranged over the casing between bolt head and bottom plate. According to the invention, there is disposed over this helical spring a further casing which at the lower edge is flanged inwardly and therewith is anchored by the helical spring. This casing in the upper area has one or more J-shaped notches, depending on the number of pins arranged in the bore holes of the part. These pins are inserted in the upwardly open notches and through a simple turning of the casing the part is secured to the fastener like a type of bayonet locking.